New reduced-temperature ceramic fuel cells with dual-ion conducting electrolyte and triple-conducting double perovskite cathode

Abstract

As a new electrolyte category, dual-ion electrolytes show the advantages of both oxygen ion conducting electrolytes and proton-conducting electrolytes to provide favorably low ohmic resistance at 450–650 °C without external gas humidification, while the insufficient activity of conventional cathodes has become the main concern for practical applications. Here, we report a triple-conducting double perovskite oxide Sr₂Sc_0.1Nb_0.1Co_1.5Fe_0.3O_6−δ (SSNCF) as a novel cathode for dual-ion solid oxide fuel cells (SOFCs). We further report a method based on an oxygen ion blocking technique in combination with a hydrogen permeability test for determining the proton conductivity in SSNCF. The results indicate the triple-conducting (H⁺|O²⁻|e⁻) capability of the perovskite with a Grotthuss mechanism for the proton diffusion. A cell with a thin-film BZCYYb electrolyte and an SSNCF cathode delivered peak power densities (PPDs) of 840 and 732 mW cm⁻², respectively, at 650 and 600 °C, superior to most other similar cells with different cathodes. Compared with Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF), the non-conflicting oxygen ion and proton diffusion channels in the SSNCF cathode significantly improved the performance of dual-ion SOFCs, where oxygen ions and protons diffuse through oxygen vacancies (vehicle mechanism) and lattice oxygen (Grotthuss mechanism), respectively. This finding highlights the potential to attain further performance enhancements for reduced-temperature SOFCs through the adoption of dual-ion electrolyte and triple-conducting cathode.